The advent of powerful, low-cost minicomputers enabled the evolution from centralized mainframe computer architectures to distributed computer architectures connected over high-speed data networks. Distributed computer architectures now range from local networks of computers within a single office, to wide-area networks covering miles, to satellite transmission systems covering entire global regions.
In contrast to distributed computer architectures, information databases have primarily remained in a centralized architecture. Database information is therefore typically disseminated to the distributed computers over communication data links. Thus, modern distributed computer systems often require the installation of high-speed data links to transmit information between processing sites. To meet these transmission requirements, high-speed data networks have been developed to link centralized information databases with distributed computer processing sites. Installation of high-speed data links, however, often requires costly and time consuming setup of high-capacity communication lines. Moreover, deployment of high-speed data links in remote field locations not served by the existing communication infrastructure is extremely difficult.
Today's communication infrastructure also includes various communication systems intended to serve other communication needs. For example, broadcast and cable television systems enable television programming to reach millions of viewers. In comparison, the public telephone network allows one subscriber to connect with another subscriber. Cellular telephone networks have extended traditional telephone service beyond the home and office to mobile subscribers. In addition, orbiting earth satellites can communicate with virtually unlimited numbers of users over large geographical areas, including areas not reached by traditional terrestrial communication systems. Service providers have also made extensive local and wide-area computer network systems accessible to the public. Such computer networks now allow users access to on-line news, sports, video and audio programming, information databases, and other computer resources such as the Internet.
These communication system are primarily designed to operate as an independent system with a transmission bandwidth capacity appropriate to serve the intended application. For example, telephone systems are primarily designed to handle low-bandwidth voice and data traffic. Accordingly, telephone systems typically support relatively low-bandwidth transmission at 9.6 kilo-bits per second (kbps). In comparison, computer networks designed to process real-time data or handle large amounts of digital data, such as an information database or graphical images, usually operate at a higher transmission bandwidth. A typical Ethernet computer network, for example, transmits at 10 megabits-per-second (mbps) for enhanced networks. Satellite communication systems designed to transmit full-motion digital video images may require even higher bandwidth equipment capable of transmitting 10 mbps or more.
In addition, communication systems may employ different methodologies to distribute information. Telephone networks primarily form point-to-point connections to connect a single subscriber to another subscriber. Computer networks typically allow a number of network nodes to access a number of other network nodes. In comparison, broadcast systems, such as a television or satellite broadcast system, typically allow one communication source to communicate with a large number of receivers.
The differences between communication systems in bandwidth rates and distribution methodology limits the interconnection and integration of heterogenous communication systems. For example, communication systems of different bandwidth rates typically cannot be connected without compensating for their different transmission rates. A 2 Mbps communication network, for example, cannot directly handle the volume of data transmitted from a faster 10 mbps system. In addition, consideration should also be given to the different manner in which systems disseminate information. Communications transported via broadcast systems are typically modified to integrate with point-to-point communication systems. Compatibility issues thus arise when interconnecting systems with different bandwidth rates and different distribution schemes. Connectivity between different communication systems may therefore be limited.
Furthermore, communication systems suffer from inherent transmission propagation delays associated with transmitting information over long distances and processing delays in distributing updated information across the system. For example, transmitting a data signal up to a geosynchronous satellite orbiting 35786 kilometers above the earth's equator and back down to a receiving earth station incurs about a quarter second transmission propagation delay. Transmitting a return signal from the receiving earth station incurs another quarter second delay. In addition to transmission propagation delays, distributed information systems may also incur processing delays in distributing updated information to users. A typical distributed information system requires users to specifically request or poll the information source to receive updated information. Waiting for a specific polling request, however, delays the distribution of updated information. While transmission propagation delays are inherent to the transmission of signals and cannot be eliminated, a communication system architecture and protocols can be implemented to minimize the effects of processing delays in distributing updated information to users.